1. Field of the Invention
The invention relates in general to a controlling circuit for a communication port, and more particularly to a smart controlling circuit for a communication port.
2. Description of the Related Art
A communication port (COM PORT) is a general purpose communication protocol between electronic devices and has the features of simplicity and distant communication. The COM PORT is also used for connecting the meters of industrial instruments and improving the driving and connection.
Examples of the COM PORT include RS-232, which has 9 pins each having different function. The ninth pin is a ring indicator (RI) pin normally used for receiving an RI signal. Sometimes, a voltage of 5V or 12V is outputted via the RI pin. According to the conventional method, the RI pin and a voltage of 5V or 12V are manually short-circuited by a jumper such that the voltage of 5V or 12V is outputted via the RI pin.
However, for each manual adjustment, the host has to be disassembled so that the jumper is used for adjusting the RI pin to select one among the three states of the RI signal, the 5V voltage and the 12V voltage. However, such method is inconvenient to the user, and adjustment error may occur during each manual adjustment.